In Order To Fight This Boss You Must Unlock "The Three Sisters" Quest By Rebuilding The Trill-Bot 4000.
After Completing The Above Achievement, This Robot Gives You A Quest To Go Defeat The Three Sisters.
- The Lair Of The Sisters Is Located In The Sundered Battlefield.
You Must Defeat The Three Sister Individually, Then Go Back To The Starting Area And Step Onto The Fountain.
- The Nearby Torches Are Lit Upon Defeating Each Of Them
- This Will Teleport You To The Boss Arena, Where You Must Defeat All Three Together.
- The Three Sisters Are Much Harder In This Boss Fight Than The Previous Iteration Of Each Was.
The Achievement Pops Mid-Fight When You Kill Marishka.
Good Luck!